388 research outputs found
Relay-Assisted User Scheduling in Wireless Networks with Hybrid-ARQ
This paper studies the problem of relay-assisted user scheduling for downlink
wireless transmission. The base station or access point employs hybrid
automatic-repeat-request (HARQ) with the assistance of a set of fixed relays to
serve a set of mobile users. By minimizing a cost function of the queue lengths
at the base station and the number of retransmissions of the head-of-line
packet for each user, the base station can schedule an appropriate user in each
time slot and an appropriate transmitter to serve it. It is shown that a
priority-index policy is optimal for a linear cost function with packets
arriving according to a Poisson process and for an increasing convex cost
function where packets must be drained from the queues at the base station.Comment: 14 pages, 5 figures, submitted to the IEEE Transactions on Vehicular
Technology in October 2008, revised in March 2009 and May 200
The Impact of Channel Feedback on Opportunistic Relay Selection for Hybrid-ARQ in Wireless Networks
This paper presents a decentralized relay selection protocol for a dense
wireless network and describes channel feedback strategies that improve its
performance. The proposed selection protocol supports hybrid
automatic-repeat-request transmission where relays forward parity information
to the destination in the event of a decoding error. Channel feedback is
employed for refining the relay selection process and for selecting an
appropriate transmission mode in a proposed adaptive modulation transmission
framework. An approximation of the throughput of the proposed adaptive
modulation strategy is presented, and the dependence of the throughput on
system parameters such as the relay contention probability and the adaptive
modulation switching point is illustrated via maximization of this
approximation. Simulations show that the throughput of the proposed selection
strategy is comparable to that yielded by a centralized selection approach that
relies on geographic information.Comment: 30 pages, 9 figures, submitted to the IEEE Transactions on Vehicular
Technology, revised March 200
A Free Space Optic/Optical Wireless Communication: A Survey
The exponential demand for the next generation of services over free space optic and wireless optic communication is a necessity to approve new guidelines in this range. In this review article, we bring together an earlier study associated with these schemes to help us implement a multiple input/multiple output flexible platform for the next generation in an efficient manner. OWC/FSO is a complement clarification to radiofrequency technologies. Notably, they are providing various gains such as unrestricted authorizing, varied volume, essential safekeeping, and immunity to interference.
Multi-radio cooperative ARQ in wireless cellular networks: a MAC layer perspective
Multi-Radio Cooperative Automatic Retransmission Request (MCARQ)
schemes are introduced in this paper within the context of hybrid networks
which combine long-range and short-range communications. Since the number of
wireless devices is incessantly increasing, it is frequently possible to establish a
spontaneous cooperative cluster in the close proximity of any wireless device.
These devices forming the cluster are connected to both a cellular-based network
such as WiMAX, 3G, or LTE and a short-range network based on technologies
such as WLAN, Zigbee, Bluetooh, or UWB, among other possibilities. The main
idea behind the proposed MC-ARQ scheme is that, upon transmission error
through the cellular interface, retransmission can be requested to the wireless grid
surrounding the destination device using the short-range interface instead of the
primary cellular link. Therefore, besides the cooperative diversity attained with CARQ
schemes, the traffic load in the cellular interface is reduced benefiting thus a
high number of users and reducing both energy consumption and interference.
The Persistent Relay Carrier Sensing Medium Access (PRCSMA) protocol is
presented as an example of solution for the MAC layer in this emerging new topic.Postprint (published version
Radio Communications
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